Baking enamels from alkyd resins and polymethylol derivatives of substituted guanamines



U it

BAKING ENAMELS FROM ALKYD RESINS AND POLYMETHYLOL DERIVATIVES OF SUBSTI- TUTED GUANAMINES Stuart H. Rider, Longmeadow, Thomas Anas, Springfield,

and George L. Fraser, North Wilbraham, Mass, assignors to Monsanto Chemical Company, St. Louis, Mo., a corporation of Delaware No Drawing. Application March 16, 1954, Serial No. 416,696

6 Claims. (Cl. 260-21) This invention relates to baking enamels. More particularly, this invention relates to alcohol-free baking enamels.

Baking enamels comprising a free-flowing organic solvent solution of a major amount of an alkyd resin and a g tes Patent ()1 lesser amount of an alkylated methylol derivative of melaconcentration of the alkylated derivative in the alkyd resin increases. At room temperature the reaction proceeds at a comparatively slow rate but, even so, resin solution stability is seriously allected unless the concentration of the alkylated derivative in the alkyd resin is kept low. Thus, for example, if an alkyd resin and an alkylated methylol derivative of melamine are dissolved in an amount of an aromatic hydrocarbon solvent suificient to provide an initially free-flowing solution, it will normally be found that gellation occurs within a comparatively short time (c. g. 3-5 weeks). If, on the other hand, an appropriate amount of the aromatic hydrocarbon is replaced with an aliphatic alcohol, the baking enamel is stabilized because of the greater solvency power of the aliphatic alcohol for the alkylated derivative and the alkyd resin. Solutions of alkyd resins and alkylated methylol derivatives of melamine in suitable mixtures of aromatic hydrocarbons and aliphatic alcohols can be stored for a year or more without gellation. Consequently, conventional baking enamels normally contain aliphatic alcohols. The alcohols contained in such enamels are irritating to workmen and also generally impart an unpleasant odor to the enamel. In addition, the alcohols are relatively expensive ascompared with aromatic hydrocarbons such as xylol and thus materially increase the cost of the baking enamel.

The problem of alcohol content cannot be completely overcome even if the aliphatic alcohol is eliminated and the baking enamel is used shortly after preparation. The alkylated methylol derivatives are prepared by reacting an aliphatic alcohol with a methylol derivative of melamine and, as a practical matter, such alkylated derivatives, even ice alkyd resin having an acid number of less than about 15 and a ditrior tetramethylol derivative of an aryl or aralkyl guanamine in a suitable alcohol-free organic solvent.

The following examples are given in illustration and are not intended as limitations on the scope of this invention. Where parts are mentioned, they are parts by weight.

EXAMPLE I Preparation of methylol derivatives Form a slurry by adding about 200 parts of powdered benzoguanamine to about 325 parts of an aqueous 37% solution of formaldehyde. Adjust the pH of the slurry to about 8 with a. dilute solution of sodium hydroxide.

Form the tetramethylol derivative of benzoguanamine by heating the slurry at a temperature of about 70 C. with agitation until the benzoguanamine is dissolved and a clear solution is formed, continuing the agitation and heating for about 20 minutes after the solution clears. At the end of this time add an equal volume of water and allow the diluted solution to cool. On standing, the tetramethylol derivative of benzoguanamine is precipitated in the form of fine crystals. Recover the precipitate by filtration, wash and dry the same.

Prepare the dimethylol derivative of benzoguanamine by reacting about 200 parts of benzoguanamine with about lparts of a 37% aqueous solution of formaldehyde in accordance with the above described procedure.

In similar fashion, react about 200 parts of phenylacetoguanamine with 325 parts of a. 37% aqueous solution of formaldehyde in order to form the tetramethylol derivative' of phenylacetoguanamine. Similarly, react about parts of melamine with 325 parts of a 37% aqueous solution of formaldehyde in order to prepare the tetramethylol derivative of melamine.

Prepare a plurality of baking enamels, each containing one of the above-described derivatives. In preparing each enamel, heat a solution of about 100 parts of an alkyd resin in about 200 parts of an aromatic hydrocarbon solvent such as xylol to a temperature of about 50 C. and, with agitation, add thereto about 20 parts of one of the described methylol derivatives. Use any suitable alkyd resin having an acid number of less than about 15 such as an intercondensation product of about 25 parts phthalic anhydride, 40 parts glycerol and 35 parts soyabean oil fatty acids. An alkyd resin of this composition will have an acid number of about 8.

The di-and tetramethylol derivatives of benzoguanamine and the tetramethylol derivative of phenylacetoguanamine will dissolve in their respective alkyd resin solutions to form baking enamels.

Flow portions of each of the methylol guanaminecontaining baking enamels on glass plates and bake for about 20 minutes at a temperature of about C. Strong, clear and durable films are formed. The baking enamels have satisfactory storage stability as evidenced by the fact that they are still free-flowing at the end of a three months storage period.

By way of contrast, when the tetramethylol derivative of melamine is added to the alkyd resin solution, it remains insoluble and forms into lumpy curds which will not dissolve in the alkyd resin solution even on prolonged agitation at a temperature of about 100 C.

The methylol derivatives which can be blended with alkyd resins to form the baking enamels of the present invention are the di-, triand tetramethylol derivatives of aryl gunanamines and aralkyl guanarnines having 1-4 carbon atoms in the alkyl radical. Representative guan- Patented Dec. 17,1957

amines that may beused-to prepare the methylol derivatives include-benzoguanamine, o-tolyl guanamine; o-xylol guanamine, phenylacetoguanamine, phenyl propionoguanamine, valerog uanamine (2ph'enylbutyl-4,6-diamino-1,3,- S-triazine), tolyl acetoguanamine, etc; Mixtures-of two" or more methylol derivatives may beusedif'desircd;

In preparing the methylol derivatives, from about 2-4 mols of formaldehyde or a polymer thereof, suchas paraforrnaldehyde, trioxymethylene, etc; should be reacted with each mol of guanamine; The-methylol derivatives are easilyprepared byreacting formaldehyde or a polymer thereof with the guanamine'with. agitation in aqueous solution at a temperature of about 50-100 C. under alkaline conditions, the heating and"agitation being'co'ntinued for a comparatively short time, sucl 1 ;as,s20+3.0.'minutes;.ater the last of the. guanamine has. gone into: solution. It is Pr f ra le. to:di.1ute.. the reaction mixture-with:azrelatively' large. excessrofi water t .the..-end..of thereaction .andito; allow thoiluted. mixture. to'coolinordertocause the. Pre+ cipitation of the methylol derivative. innthaforrn-tofii fine; granular crystals.

A. wide variety of alkyd, resins;havingzanracidinumber: ofless. than bo 1.5 arezavailahle andzarewell-known. to those skilled in theart. The kydresins;usefuliimthe. preparation. of. baking. enamels: are; preferably prepared. by intercondensing a. dicarboxylic. acid .and: a. monomerboxylic fatty: acid with a pol-yhydric. alcohol .contarmng3 or more hydroxyl groups. If desired, a dihydricraleoholh. canbe. 'intercondensed with at:monocarboxyliczfatty aacid and. apolycarboxylic acid containingfisorsmore carboxyhc-j acid. groups. Representative. polycarboxylic; acids that may. e. used. include -succinie'acid .glutarie. acid; .adipic. acid, sebacic. acid, phthalic: acid;.biphenylidicarhoxylic acid, theanhydrides-nhereof; adductsr ofjlzdrdiencsiandi Illustrative polyhydric alcohols.

maleicanhydride, etc. that, maybensed include. sorbitol, manmtol, pcntaerythritol, glycero1,.. trimethylolr ethane; trimethyl'ol' propane;

etc. Suitable. monocarboxylic; fatty-: acids: includesoyabean oil fatty acids, coconut oil fatty. acids, dehydrated"- castor oil fatty acids, linseed oil. fatty acids, etc. The alkyd resin should comprise about 30-60% by weight of monocarboxylic fatty acidti. 'e., should-have a 30-60% oil length).

The organic solvents to be used ill-accordance. with the. present invention are the, aroma ic, hydrocarbons-and mixtures of such aromatic hydrocarbons with each other or with aliphatic hydrocarbons. When an aliphaitichy drocarbon is mixed with an aromatic hydrearbon.,the; aromatic hy roc rbon ho l comprise h maior por ion of'th'e mixture. Nume ous... examples of. such. solvents. are well-known to.thos e skilledin theart. Representative of the aromatic hydrocarbon, solventsarebenzene, toluene; xylol, etc. and representativeof thealiphatic hydrocarbons are hexane, heptane, etc. The proportionsofi the. alkyd. resin, m y l. deriv tive solven may e: v r ed: as desired but, generally speaking,.itisrpreferable. towuse. a. composition mp sing. .on.a.so1ids basis, from about 70-95% alkyd resin and, correspondingly, fromahqnt. 30 me y l d rivativ Th mo nt'of. solvent to. be. c o d he. ufiicicnt to. provide a. free-flowing; sole. tion. of the two ingredients.

In P pa h a ingenamel t e. yd r sinishould first be dissolved inthe-solvent. The methylol: derivative;

' driers, accelerators, fillers, etc.

4- should then be added to this solution. This is of importance-because the methylol derivatives of the aryl and derivative with agitation and to heat the alkyd resin solution to a moderate extent during. the addition. Preferably, temperatures of about 40-60 C. are used. The baking enamels of the present invention can be cured on being heated .at' temperatures of about. 120-180" C. for periods of time varying from about 15. minutesto one hour.

Various other conventional additives may be used if desired, such as pigments or other suitable colorants, The additives may be added to the alkyd resin solution prior to, simultaneously with, or subsequent to the addition of the methylol derivative.

What is claimed is:

1. An alcohol-free baking enamel consisting essentially of a free-flowing solution of about 70-95 parts by weight of an alkyd resin having an oil length of about -60% and an acid numbcrof less than about 15 and, correspondingly, about 30-5 parts by weight of a compound taken from thegroup consisting of di-, triand tetramethylol derivatives of aryl guanamines and aralkyl guanamines having 1-4 carbon atoms in the alkyl radical in a solvent taken. from the group. consisting of aromatic hydrocarbon solvents and mixtures of a major amount of an aromatic hydrocarbon solvent with av minor amount of an aliphatic hydrocarbon solvent, said compounds being crystalline materials prepared by; heating l.mol of the guanamine with 2-4 mols offormaldehydeat temperatures .of 5 0-100 C. in an aqueousalkaline solution.

2. .A baking enamel as. in claim 1. wherein the methylol derivative is a methylolderivative of an aryl guanamine.

3; A baking enamelv as in claim 2 wherein the aryl guanamine is benzoguanarnine.

4. Abaking enamel as. inclaim l wherein the methylolderivative is a methylol derivative of an aralkyl guanamine.

5 A baking enamel as. inclaim 4 wherein the aralkyl guanarnine is phenylacetoguanamine.

6.. A. process for. preparing. an alcohol-free baking enamel which consists. essentially of dissolving about -95 parts. by vveightof an alkyd resin having an oil length ofabout 30-60% and: an acid number ofv less. than about l5.v in asuflicient amount of asolvent taken from the group .consistingv of aromatic. hydrocarbon solvents;and.

mixturcabfamajor amount of anaromatic hydrocarbon solvent, with a-mincr. amount of an, aliphaticv hydrocarbon solvent. to form aafree-flowing solution and then adding to said solution, with agitation andmoderate heating, from about 30-5 parts by weight-of a compound takensfrom the group-consisting of di-, triandtetramethylolderiv atives. of, aryl .guauamincs. and aralkyl guanamines "having- 1-4.carbon.atoms, in the alkyl. radical, saiclicompounds being crystalline materials prepared by heating 1 molof the guanarnine with.2-4mols.-of formaldehyde at temperatures of 50-100- C. in an aqueousalkalinesolution;

References Cited. in the file of thispatent UNITED STATES PA IENTS Spencer Dec. 25, 1951 

1. AN ALCOHOL-FREE BAKING ENAMEL CONSISTING ESSENTIALLY OF A FREE-FLOWING SOLUTION OF ABOUT 70-95 PARTS BY WEIGHT OF AN ALKYD RESIN HAVING AN OIL LENGTH OF ABOUT 30-60% AND AN ACID NUMBER OF LESS THAN ABOUT 15 AND, CORRESPONDINGLY, ABOUT 30-5 PARTS BY WEIGHT OF A COMPOUND TAKEN FROM THE GROUP CONSISTING OF DI-,TRI- AND TETRAMETHYLOL DERIVATIVES OF ARYL GUANAMINES AND ARALKYL GUANAMINES HAVING 1-4 CARBON ATOMS IN THE ALKYL RADICAL IN A SOLVENT TAKEN FROM THE GROUP CONSISTING OF AROMATIC HYDROCARBON SOLVENTS AND MIXTURES OF A MAJOR AMOUNT OF AN AROMATIC HYDROCARBON SOLVENT WITH A MINOR AMOUNT OF AN ALIPHATIC HYDROCARBON SOLVENT, SAID COMPOUNDS BEING CRYSTALLINE MATERIALS PREPARED BY HEATING 1 MOL OF THE GUANAMINE WITH 2-4 MOLS OF FORMALDEHYDE AT TEMPERATURES OF 50-100* C. IN AN AGUEOUS ALKALINE SOLUTION. 